1. Field of the Invention
The present invention relates to an intake manifold for a multi-cylinder air-fuel mixture suction type engine.
More particularly, it relates to an improved design for such an intake manifold, wherein the intake manifold body is formed into a hollow shell-shape and has an air-fuel inlet mixture opening formed on a wall thereof where a carburetor is installed and a large air-fuel mixture outlet openng which is formed through the greater part of the back face thereof and extended over all of the intake ports of the engine.
2. Prior Art
Generally, as compared with a branched type intake manifold, the above-mentioned intake manifold has such an advantage that it can be produced more readily and cheaper by a die casting because of its simple shape. And the prior art formation method of the air-fuel mixture inlet opening in the intake manifold is proposed, for example in U.S. Pat. No. 3,667,432 as shown in FIG. 6 and in U.S. Pat. No. 4,320,726 as shown in FIG. 7.
The intake manifold 101 of the engine E.sub.1 shown in FIG. 6 has the air-fuel mixture inlet opening 111 formed upwardly in the middle portion of the upper wall of its body 110. However, since the liquid fuel particles in the air-fuel mixture sucked into the intake manifold body 110 from the carburetor 102 are apt to flow much more into the middle intake port 114b than into other intake ports 114a,114c due to its arrangement, the density of the mixture in the middle cylinder becomes over rich enough to cause an imperfect combustion and the density of the mixture in both sides cylinders becomes lean enough to cause a misfire.
On the other hand, the intake manifold 201 shown in FIG. 7 has the mixture inlet opening 211 which is formed leftwards in the left-side end wall of the bilaterally elongated body 210. The intake manifold 201 has such an advantage that the dimension of the engine E.sub.2 can be made smaller because the carburetor 202 is disposed thereon without protruding outwardly beyond the manifold body 210. However, since the liquid fuel particles in the air-fuel mixture sucked into the manifold body 210 are apt to flow much more into the intake port 214c disposed at the right end thereof than into other intake ports 214a,214b by their kinetic inertia, the density of the mixture in the right end cylinder becomes over rich enough to cause an imperfect combustion and the density of the mixture in the middle and the left side cylinders becomes lean enough to cause a misfire. Especially, the misfire is caused more frequently in the left end cylinder than in the both ends cylinders shown in FIG. 6.